684 
J. DAVIDSON. 
From each of the thoracic ganglia a pair of nerves is given 
off laterally, which pass into the legs [n. l^.). These 
nerves bifurcate before entering the coxrn. From the posterior 
end of the abdominal ganglion a stout post-abdominal nerve 
(p.) extends in the median line beneath the alimentary canal, 
almost to the posterior end of the body. At its extremity, 
beneath the vagina, it expands into an irregular club-shaped 
post-abdominal ganglion (p. g.), from which nerves pass to 
innervate the vagina and muscles of the terminal abdominal 
segments. Several nerves are given off along the length of 
the post-abdominal nerve. They arise more or less irregularly 
in paii’S, and pass in a post-lateral direction to the abdominal 
segments, especially innervating the longitudinal bauds of 
muscles on the floor of the body. 
c. The Respiratory System (PI. 38, fig. 5 ; PI. 41, fig. 39). 
The respiratory system consists of a dorsal and ventral 
system of tracheal tubes, the main trunks from which com- 
municate with the exterior by means of nine paii’s of 
spiracles. Each spiracle consists of a small opening sur- 
rounded by a chitinous ring. Each of the first seven 
abdominal segments bears a pair of spiracles, which ai’e 
situated on the ventral surface, near the lateral margins of 
the body. 
The two pro-thoracic spiracles are situated external to the 
coxae on the ventral surface of the prothorax, near its 
posterior margin. Two similar meta-thoracic spiracles (m. s.) 
are situated near the anterior border of the metathorax- 
There are no spiracles on the mesothorax. 
Eorsal Tracheal System. — Leading from each spiracle 
is a short tracheal trunk {s. r.), which bifui-cates into a 
dorsal {d. h.) and a ventral {v. b.) tracheal branch. The 
dorsal branches from the spiracles pass upwards, more 
or less parallel to one another, along the lateral walls of 
the body to the dorsal surface, and then inwards towards 
the dorso-rnedian line. At some distance from the median 
